{"product_id":"lower-unit-fill-drain-plug-washer-fits-johnson-evinrude-omc-20-300hp-replaces-311598-18-4248-9-60408","title":"Lower Unit Fill Drain Plug Washer – Fits Johnson Evinrude OMC 20-300HP (Replaces 311598, 18-4248, 9-60408)","description":"\u003cstyle\u003e\n  .ss-table-wrap { overflow-x:auto; -webkit-overflow-scrolling:touch; }\n  table.ss-table { width:100%; border-collapse:collapse; min-width:640px; }\n  table.ss-table th, table.ss-table td {\n    padding:10px 12px; border:1px solid #e5e7eb; text-align:left; vertical-align:top;\n  }\n  table.ss-table th {\n    white-space:nowrap;\n    word-break:normal;\n    letter-spacing:normal;\n    font-weight:600;\n    background:#f8fafc;\n  }\n  @media (max-width:480px){\n    table.ss-table th, table.ss-table td { padding:8px 10px; font-size:14px; }\n  }\n\u003c\/style\u003e\n\n\u003ch2\u003eProduct Details\u003c\/h2\u003e\n\u003cp\u003eThis \u003cstrong\u003eLower Unit Fill Drain Plug Washer\u003c\/strong\u003e is engineered for Johnson Evinrude OMC outboard engines ranging from 20 to 300 HP. Compatible with a wide range of 2-cylinder, 3-cylinder, V4, and V6 configurations spanning model years 1975 through 2006, this drain screw gasket ensures a reliable seal during lower unit service intervals.\u003c\/p\u003e\n\u003cp\u003eDirect aftermarket replacement for OEM part numbers 311598, 18-4248, 9-60408, and 3852105 across Johnson\/Evinrude Outboard, OMC Stern Drive, Mallory, and Volvo Penta applications.\u003c\/p\u003e\n\u003cul\u003e\n  \u003cli\u003eSeals lower unit fill and drain plug points to prevent gear oil leakage\u003c\/li\u003e\n  \u003cli\u003eDesigned for both 2-stroke and 4-stroke outboard applications\u003c\/li\u003e\n  \u003cli\u003eReplace during every lower unit oil change for optimal protection\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003ePart Number Matrix\u003c\/h2\u003e\n\u003cp\u003eUse this matrix to confirm equivalent references across OEM and aftermarket.\u003c\/p\u003e\n\u003cdiv class=\"ss-table-wrap\"\u003e\n  \u003ctable class=\"ss-table\" aria-label=\"Part Number Matrix\"\u003e\n    \u003cthead\u003e\n      \u003ctr\u003e\n        \u003cth\u003eBrand\u003c\/th\u003e\n        \u003cth\u003ePart Number\u003c\/th\u003e\n      \u003c\/tr\u003e\n    \u003c\/thead\u003e\n    \u003ctbody\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eJohnson\/Evinrude Outboard\u003c\/td\u003e\n        \u003ctd\u003e311598\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eMallory\u003c\/td\u003e\n        \u003ctd\u003e9-60408\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eSierra\u003c\/td\u003e\n        \u003ctd\u003e18-4248\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eOMC Stern Drive\u003c\/td\u003e\n        \u003ctd\u003e311598\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eOMC Stern Drive\u003c\/td\u003e\n        \u003ctd\u003e3852105\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eVolvo Penta\u003c\/td\u003e\n        \u003ctd\u003e3852105\u003c\/td\u003e\n      \u003c\/tr\u003e\n    \u003c\/tbody\u003e\n  \u003c\/table\u003e\n\u003c\/div\u003e\n\n\u003ch2\u003eEngine \u0026amp; Model Compatibility\u003c\/h2\u003e\n\u003cp\u003eConfirm your engine model\/year in the table below.\u003c\/p\u003e\n\u003cdiv class=\"ss-table-wrap\"\u003e\n  \u003ctable class=\"ss-table\" aria-label=\"Engine \u0026amp; Model Compatibility\"\u003e\n    \u003cthead\u003e\n      \u003ctr\u003e\n        \u003cth\u003eBrand\u003c\/th\u003e\n        \u003cth\u003eModel\u003c\/th\u003e\n        \u003cth\u003eRated HP\u003c\/th\u003e\n        \u003cth\u003eYears\u003c\/th\u003e\n      \u003c\/tr\u003e\n    \u003c\/thead\u003e\n    \u003ctbody\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eJohnson Evinrude\u003c\/td\u003e\n        \u003ctd\u003e2-Cyl. Crossflow\u003c\/td\u003e\n        \u003ctd\u003e20–35 HP\u003c\/td\u003e\n        \u003ctd\u003e1980–2005\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eJohnson Evinrude\u003c\/td\u003e\n        \u003ctd\u003e3-Cyl. Loopcharged\u003c\/td\u003e\n        \u003ctd\u003e25, 30, 35 HP\u003c\/td\u003e\n        \u003ctd\u003e1996–2001\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eJohnson Evinrude\u003c\/td\u003e\n        \u003ctd\u003e2-Cyl. Crossflow\u003c\/td\u003e\n        \u003ctd\u003e25–28 HP\u003c\/td\u003e\n        \u003ctd\u003e1978–1997\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eJohnson Evinrude\u003c\/td\u003e\n        \u003ctd\u003e2-Cyl. Loopcharged\u003c\/td\u003e\n        \u003ctd\u003e40–50 HP\u003c\/td\u003e\n        \u003ctd\u003e1989–2005\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eJohnson Evinrude\u003c\/td\u003e\n        \u003ctd\u003e2-Cyl. Loopcharged\u003c\/td\u003e\n        \u003ctd\u003e40–60 HP\u003c\/td\u003e\n        \u003ctd\u003e1975–1988\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eJohnson Evinrude\u003c\/td\u003e\n        \u003ctd\u003e3-Cyl. Loopcharged\u003c\/td\u003e\n        \u003ctd\u003e60–75 HP\u003c\/td\u003e\n        \u003ctd\u003e1975–1988\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eJohnson Evinrude\u003c\/td\u003e\n        \u003ctd\u003e2-Cyl. Loopcharged\u003c\/td\u003e\n        \u003ctd\u003e40–60 HP\u003c\/td\u003e\n        \u003ctd\u003e1975–2006\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eJohnson Evinrude\u003c\/td\u003e\n        \u003ctd\u003e3-Cyl. Loopcharged\u003c\/td\u003e\n        \u003ctd\u003e60–75 HP\u003c\/td\u003e\n        \u003ctd\u003e1975–2001\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eJohnson Evinrude\u003c\/td\u003e\n        \u003ctd\u003eV4\/V6 \"O\" Type\u003c\/td\u003e\n        \u003ctd\u003e\u003c\/td\u003e\n        \u003ctd\u003e1979–2006\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eJohnson Evinrude\u003c\/td\u003e\n        \u003ctd\u003eV4\/V6 \"M\" Type\u003c\/td\u003e\n        \u003ctd\u003e\u003c\/td\u003e\n        \u003ctd\u003e2002–2006\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eJohnson Evinrude\u003c\/td\u003e\n        \u003ctd\u003e\"M2\" Type, 60° V6\u003c\/td\u003e\n        \u003ctd\u003e150–200 HP\u003c\/td\u003e\n        \u003ctd\u003e\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eJohnson Evinrude\u003c\/td\u003e\n        \u003ctd\u003e\"M2\" Type, 90° V6\u003c\/td\u003e\n        \u003ctd\u003e200–300 HP\u003c\/td\u003e\n        \u003ctd\u003e\u003c\/td\u003e\n      \u003c\/tr\u003e\n    \u003c\/tbody\u003e\n  \u003c\/table\u003e\n\u003c\/div\u003e\n\n\u003ch2\u003eTechnical Specs\u003c\/h2\u003e\n\u003cdl\u003e\n  \u003cdt\u003eOEM Part Number\u003c\/dt\u003e\n  \u003cdd\u003e311598\u003c\/dd\u003e\n  \u003cdt\u003eInterchange Numbers\u003c\/dt\u003e\n  \u003cdd\u003e18-4248, 9-60408, 3852105\u003c\/dd\u003e\n  \u003cdt\u003eApplication\u003c\/dt\u003e\n  \u003cdd\u003eLower Unit Fill \u0026amp; Drain Plug Seal\u003c\/dd\u003e\n  \u003cdt\u003eFitment Range\u003c\/dt\u003e\n  \u003cdd\u003eJohnson Evinrude OMC 20–300 HP Outboards\u003c\/dd\u003e\n  \u003cdt\u003eModel Years\u003c\/dt\u003e\n  \u003cdd\u003e1975–2006\u003c\/dd\u003e\n\u003c\/dl\u003e\n\n\u003ch2\u003eWhat's in the Box\u003c\/h2\u003e\n\u003cul\u003e\n  \u003cli\u003e\u003cstrong\u003e1× Gasket 311598\u003c\/strong\u003e\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003eInstallation Notes\u003c\/h2\u003e\n\u003col\u003e\n  \u003cli\u003eEnsure engine is off and lower unit is cool to the touch before beginning service.\u003c\/li\u003e\n  \u003cli\u003ePosition boat or tilt engine so lower unit is accessible and level.\u003c\/li\u003e\n  \u003cli\u003eRemove the existing drain plug and allow gear oil to fully drain into a suitable container.\u003c\/li\u003e\n  \u003cli\u003eInspect the old washer for signs of wear, compression set, or cracking.\u003c\/li\u003e\n  \u003cli\u003eClean the plug threads and sealing surface on the lower unit housing.\u003c\/li\u003e\n  \u003cli\u003ePlace the new washer onto the drain plug, ensuring it seats evenly.\u003c\/li\u003e\n  \u003cli\u003eReinstall the drain plug and tighten to manufacturer-specified torque to prevent over-compression or leakage.\u003c\/li\u003e\n  \u003cli\u003eRefill the lower unit with the correct grade and quantity of gear oil per your service manual.\u003c\/li\u003e\n  \u003cli\u003eInstall the fill plug with a new washer using the same procedure.\u003c\/li\u003e\n  \u003cli\u003eRun the engine briefly, then inspect both plugs for any signs of seepage.\u003c\/li\u003e\n\u003c\/ol\u003e\n\n\u003ch2\u003eTroubleshooting \u0026amp; FAQ\u003c\/h2\u003e\n\u003cdetails\u003e\n  \u003csummary\u003eHow often should I replace this washer?\u003c\/summary\u003e\n  \u003cp\u003eReplace the washer every time you perform a lower unit oil change—typically every 100 hours of operation or annually, whichever comes first. Reusing old washers increases the risk of leaks and contamination.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n  \u003csummary\u003eWill this fit both the fill and drain plugs?\u003c\/summary\u003e\n  \u003cp\u003eYes, the same washer design is used for both the fill and drain plug positions on compatible Johnson Evinrude lower units. Always replace both washers during each service interval.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n  \u003csummary\u003eWhat are the signs of a failing drain plug washer?\u003c\/summary\u003e\n  \u003cp\u003eVisible gear oil seepage around the plug, low oil levels during inspection, or milky oil indicating water intrusion are common indicators. If you notice any of these, replace the washer immediately and inspect for corrosion or thread damage.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n  \u003csummary\u003eCan I reuse the washer if it looks okay?\u003c\/summary\u003e\n  \u003cp\u003eNo. Even if the washer appears intact, it has been compressed and may not seal reliably after removal. Always use a new washer to ensure a proper seal and prevent costly lower unit damage.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n  \u003csummary\u003eWhat torque spec should I use when reinstalling the plug?\u003c\/summary\u003e\n  \u003cp\u003eConsult your engine's service manual for exact torque values, as they vary by model. Over-tightening can crush the washer and damage threads; under-tightening may cause leaks.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n  \u003csummary\u003eIs this compatible with OMC Cobra stern drives?\u003c\/summary\u003e\n  \u003cp\u003eYes, this washer crosses to OMC Stern Drive part numbers 311598 and 3852105. Verify your stern drive model and year against the compatibility table to confirm fitment.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n  \u003csummary\u003eOEM vs. Aftermarket?\u003c\/summary\u003e\n  \u003cp\u003eThis listing is an aftermarket replacement (not OEM). Built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, batch-inspected for consistency.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n  \u003csummary\u003eShipping speed \u0026amp; cost\u003c\/summary\u003e\n  \u003cp\u003eWe ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n  \u003csummary\u003eWarranty \u0026amp; returns\u003c\/summary\u003e\n  \u003cp\u003eCovered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact support with your order details. Returns are accepted within our standard window (unused \u0026amp; in original condition). See our policy page or reach out for instructions.\u003c\/p\u003e\n\u003c\/details\u003e\n\n\u003ch2\u003eSafety \u0026amp; Important Info\u003c\/h2\u003e\n\u003cul\u003e\n  \u003cli\u003eVerify images\/specifications against your original part. If anything differs—even if your model appears compatible—do not purchase.\u003c\/li\u003e\n  \u003cli\u003eThis is an aftermarket replacement, not an OEM component.\u003c\/li\u003e\n  \u003cli\u003eProfessional installation is recommended for safety and performance.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003eAbout Sea Sierra\u003c\/h2\u003e\n\u003cul\u003e\n  \u003cli\u003ePro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.\u003c\/li\u003e\n  \u003cli\u003eFast Global Fulfillment — Free standard delivery to most regions in 5–15 days.\u003c\/li\u003e\n  \u003cli\u003eManufacturer-Direct Value — Fair pricing without compromising on materials or QC.\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"SeaSierra","offers":[{"title":"Default Title","offer_id":51025914921275,"sku":"2923","price":13.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0826\/8673\/8747\/files\/WechatIMG1101_1727234955.png?v=1772975108","url":"https:\/\/seasierra.com\/products\/lower-unit-fill-drain-plug-washer-fits-johnson-evinrude-omc-20-300hp-replaces-311598-18-4248-9-60408","provider":"SeaSierra","version":"1.0","type":"link"}